Is lying common practice in negotiations?

I received an offer on my home after the first round of open houses that was over asking with a waived inspection & solid financing. It was the only offer I received.

My agent wanted to lie to the folks who made an offer and tell them we received multiple offers and to please submit best and final. I rejected that strategy & my agent insisted that it was common practice at his realty group.

I feel comfortable in my decision to not go through with that plan but was wondering if that strategy really is common place. It feels slimy to me.